Key

Names displayed are according to the Atlus (NA) version of the game. Name changes from the Asian version, if any, will appear in parentheses.

Damage:

The Damage stat dictates how much damage the shield does when used for bashing.

All shields have Blunt physical damage, apart from the Spiked shield's Slashing damage, but it is also more of a weapon than a shield.
Certain enemies are weak or strong against different damage types.

Damage Reduction %:

The Damage Reduction % of the shield. It dictates how much damage the shield mitigates while blocking.
The Damage Reduction % stats for shields are X / Y / Z:

X is Physical Damage

Y is Magical Damage

Z is Fire Damage

Guard Break Reduction:

The Guard Break Reduction determines the amount of stamina expended to block an incoming attack. A higher Guard Break Reduction also allows you to block stronger attacks without breaking guard and reduces the amount of stamina depleted from blocking attacks.

Durability:

The Durability of the shield. The effectiveness of the shield will severely deteriorate when the durability falls below 30%.

Weight:

The Weight of the shield. Note that carrying over 50% of your Equip Weight will reduce the speed of your rolls, while going over 100% will reduce your regular speed to walking and attempts to roll or backstep will leave you momentarily stunned.

Requirements:

The Requirements determines how high various Stats must be in order to wield the shield effectively.
The Requirement stats for shields are W / X / Y / Z:

W is the Strength required

X is the Dexterity required

Y is the Magic required

Z is the Faith required

While it is possible to use a shield with lower-than-required Strength, your character will suffer a severe penalty to Guard Break Reduction, thus making it easier to break your character's guard.

Footnotes

1. for instance, if you had a Catalyst in one hand, and the Dark Silver Shield in the other, and you cast Soul Arrow, Soul Arrow will do less damage. For example, without this shield equipped Soul Arrow does 214 damage on Red Eye Knight at the end of 1-3 with Magic stat at 31, and with this shield you will do 162 damage. However, if you had a Moon Sword instead of the Catalyst, the Moon sword will still do full damage.